The present invention relates to a ceiling-mounted loudspeaker and in particular to such a speaker which provides a wide included angle of uniform sound coverage over the planned listening area.
Loudspeakers for distributed paging and music systems are often placed in the ceilings of rooms and corridors and are frequently mounted in the suspended ceiling enclosure of the return-air plenum of an architectural space. Because such loudspeakers violate the structural integrity of the ceiling, they must comply with the requirements of building codes generally and, in particular, the building codes relating to fire and smoke protection.
In order to provide uniform sound coverage over a planned listening area (and in particular uniform sound coverage at ear height as a person moves away from the centerline vertical axis perpendicular to the face of the loudspeaker assembly), the coverage angle from that vertical axis must be such that the loudness of the sound, particularly in the speech intelligibility range of 1400 to 5600 Hz, must not vary (e.g., diminish) significantly at ear height as a person moves horizontally relative to (e.g., away from) that vertical axis within the planned listening area. Ideally, the speaker directivity pattern would be an oblate or flattened sphere.
The typical ceiling-mounted loudspeakers are the conventional cone-type loudspeakers facing the floor, the loudspeakers being mounted on metal grills housed in metal boxes that provide code compliance in plenum ceilings. Such assemblies provide downwardly directed cones of sound energy over included coverage angles of about 90 to 120 degrees. Thus, assuming a 12 foot ceiling, such an assembly could provide coverage to about a 7 foot radius from the centerline vertical axis perpendicular to the face (i.e., bottom) of the loudspeaker assembly. Therefore, in order to provide the desired coverage (with an appropriate overlap at the coverage edges), the loudspeakers would have to be mounted on the ceiling no more than about 12 feet apart.
In an attempt to widen the coverage angle, some conventional ceiling-mounted loudspeaker assemblies incorporate reflecting devices disposed below the face of the loudspeaker assembly. However, it has been found that too much of the sound produced by the loudspeaker diffracts around the reflecting device for it to have a significant effect in widening the coverage angle.
While conventional radial horn-type loudspeakers have been ceiling-mounted, these have not proven to be entirely satisfactory in use. Such a radial-type loudspeaker provide a desirably wide angle of coverage, but the loudness of the sound within that coverage angle is not substantially uniform at ear height and significantly diminishes as a person moves towards the axis and directly underneath the loudspeaker.
Accordingly, it is an object of the present invention to provide a ceiling-mounted loudspeaker providing sound coverage over a wide angle.
Another object is to provide such a loudspeaker which provides substantially uniform sound coverage over the planned listening area.
A further object is to provide such a loudspeaker which reduces the number of loudspeakers required for coverage of a given area relative to the number of conventional cone-type ceiling-mounted loudspeakers which would be required.
It is also an object of the present invention to provide such a loudspeaker consisting of various components, but in which only one component needs to comply with building code requirements regarding fire and smoke protection.